Oil rings are extensively used as conduit means for carrying oil or other lubricant from a reservoir to moving members, such as journal bearings, shafts, and the like. In operation, the oil ring is normally loosely disposed around the shaft and rotates as the shaft rotates, through contact with the shaft. Lubricant is carried from a sump or reservoir to the shaft, in the contours or grooves of the oil ring and by frictional attraction as the ring moves through the reservoir. The lubricant is deposited on the shaft or other member through the gravitational, frictional, and centrifugal forces inherent in the operation. Under conditions of slow rotation, the gravitational and frictional forces generally deliver a sufficient supply of lubricant; however, at higher velocities, which can be as high as 3000 to 4000 ft./min., the oil ring is either moving too fast for gravity to effect dispersion of the oil, or the centrifugal force on the ring and the oil is too great to overcome, and the oil either remains on the ring or is thrown outside of the rotational field. Thus, the lubricant does not reach the desired area, resulting in early wear and possible failure of the shaft, bearing, oil ring, or other associated members.
Rotation of the oil ring depends on a propulsive force developed between the rotating shaft and the ring. As speeds increase, a fluid film is developed, and the driving force is transmitted to the ring by this lubricant film. The situation is analogous in many ways to that in a floating ring bearing and, without a direct drive mechanism, a slippage occurs. Prior attempts to develop a higher frictional coefficient and, thus, a more positive drive mechanism, have focused on modification of the cross-sectional geometry of the ring, including both inside and outside surfaces of the ring. Such prior ring structures have included T-shaped rings where the cross of the T serves as the inside surface, rings having a generally trapezoidal cross-section where the inner ring surface is planar, and rings having a generally trapezoidal cross-section where the inner ring surface contains a single wide groove thereacross.
Factors opposing rotation of the ring are the drag on the lower portion of the ring which is submerged in the lubricant reservoir, the force required to lift the lubricant from the reservoir toward the top of the journal, and the frictional drag on the ring applied by close-running stationary surfaces, such as the sides of the ring slot in the bearing. Other factors affecting lubricant delivery include the composition of the ring and the viscosity of the lubricant used in the bearing. In addition, since a conventional oil ring rests on the upper surface of the shaft during operation and during periods of non-use, much wear results from the contact alone. When at rest, most of the lubricant drains back into the reservoir and very little lubricant protection is available for the start-up operation. Thus, until the lubricant film is re-established, early wear of the shaft, ring, bearings, and other associated members is likely to occur. This, in turn, leads to repair and replacement expenses, and the concomitant loss of operating time.